On the basis of present knowledge, it is implied that the atherosclerotic process may be prevented and possibly even reversed by reducing serum lipids and cholesterol. Polyunsaturated dietary fat has been shown to have a hypocholesteremic effect in animals and in man; however, there is a great deal of controversy as to its mechanism of action. The objective of this research project is to investigate the mechanism of the changes in plasma cholesterol levels and secretions of biliary steroids by saturated and polyunsaturated dietary fat. An experimental animal model, the minipig, with a balloon occludable Baldwin T-tube catheter positioned in the common bile duct for bile collection and sampling and a duodenal catheter for bile reinfusion will be used. This enables long term studies of bile flow and composition while keeping the enterohepatic circulation intact. The study of cholesterol and its end products, the bile acids, before they are changed into other metabolites in the gastrointestinal tract may provide more accurate information regarding the mechanisms by which dietary fats influence plasma cholesterol levels.